First, add the following line to your config.php file under the <?php line:
PHP Code:
define('SKIP_ALL_ERRORS', true);
Then, create a new style with no parent:
Styles & Templates > Style Manager > Add New Style
Parent Style: No Parent Style
Title: Default vBulletin
Allow User Selection: Yes
Save
Then browse the site using that totally default vbulletin style - do you still have the same problem?